Abstract:

The microstructure of a multi-component oil-in-water (O/W) microemulsion, to serve as a microreactor or a solubilization vehicle for food applications, has been studied using small angle scattering X-rays (SAXS) and neutron (SANS) techniques. Significant structural changes along selected aq. diln. lines in the O/W microemulsions were detd. It was found that the droplets' size is affected by increasing the water content, the oleic phase concn. and content (mixt. of R(+)-limonene and ethanol), and the nature of the surfactant (Brij 96v and Tween 60). The micellar size increases with increasing the aq. phase content in both, Brij 96v-based and Tween 60-based systems. Replacing Brij 96v by Tween 60 at const. wt. leads to larger microemulsion droplets. The increase in the surfactant concn. of these systems, as expected, leads to smaller interaction radii and to higher values of the no. particle d. Increasing ethanol content in the oleic phase (R(+)-limonene plus ethanol) decreases the effective vol. fraction, and causes redn. in the micellar size at decreasing surfactant aggregation no. as a result of its redistribution between the interfacial film and the continuous aq. phase. The SANS investigations allowed a focus on the main effects of propylene glycol (PG) and ethanol (EtOH). Both hydrophilic mols. have similar tuning properties on the microstructure. Both decrease the droplet size, render them more globular, and increase the no. of micelles. It was concluded from these results that both alcs. are partially incorporated into the interface (most of it stays in the aq. phase). The only obsd. difference in the investigated samples was that upon replacing the aq. phase partially with PG, the effective vol. fractions of the dispersed phase was decreased, while it remained unchanged when it was partially replaced by EtOH. PG and EtOH seem to influence the microstructure independently. [on SciFinder(R)]